This invention relates to the finishing of unusal shapes by an abrading process and more particularly to the contour honing of a gerotor ring which is used in conjunction with a hydraulic pump or motor.
The gerotor pump also sometimes known as a gear pump or motor has a rotating star shaped element which is slightly offset from the major axis of the unit cooperating with a stator ring. Such a pump or device is shown in two recently issued U.S. Pat. Nos. 4,200,427 and 4,181,479. This particular type pump is also sometimes referred to as a star pump. The typical assembly has a symmetrically shaped element which makes up the rotor portion and a cyclodial shaped element for the stator portion of the active parts of the pump system. In such a device the rotating element has one less tooth form on it than the mating stator thereby causing the center line or axis of the rotor to follow a path which is eccentric to the major axis of the stator. This offset causes a fixed displacement to exist between the rotor and stator. These types of devices used as both pumps and motors have been manufactured for many many years.
The finishing process for the stator in these devices has in the past consisted of a high speed grinding operation in order to achieve a surface finish that will be acceptable to give the efficiency needed to be competitive with a pump or motor of the vane or piston type. An apparatus for finishing epitrochoidal surfaces has been patented in the U.S. by the patentee, Czubak, and issued as U.S. Pat. No. 3,884,789. The system shown in this patent to hone such epitrochoidal shapes utilized, in addition to the eccentric gear driven hone, a method whereby a plating process is simultaneously going on to achieve the desired surface finish. Another U.S. Patent issued to Hoglund, U.S. Pat. No. 3,774,346, shows a honing apparatus for honing epitrochoidal surfaces. In addition, a United Kingdom Pat. No. 957,922 shows a machining method for machining the cylinder surfaces of a rotary piston engine. This shape is an epitrochoidal shape such as machined in the aforementioned patents. The major purpose of these prior art patents was to hone the usnusual shape and improve the surface finish and wear resistance characteristic of the surface so that improved efficiencies of operation could be obtained.
It is the object of my invention to improve the surface finish of a gerotor ring by abrading the internal surface of such a ring by utilizing three equally spaced honing stones. These honing stones will be mounted in a holder such that the whole assembly can reciprocate transversely to the surface of the gerotor ring while the stones are rotating.
It is further the object of this invention to have the honing stone holder assembly mounted on thrust bearings so that it can float while being rotated on an eccentric spindle arrangement and reciprocated transversely thereby imparting a spiral motion to the stones to finish the surface of the gerotor ring lobes.
Further, it is an object of this invention to have the eccentric means synchronized for controlling the path of the abrading tools in relation to the gerotor ring workpiece so that a uniform finish will be achieved on the ring. It is the further object of this invention to have the surfaces of the honing stones countoured in such a way so as to completely finish the projecting lobes of the gerotor ring.
It is a further object of this invention to have the center line or pivot axis of the honing stone tool holder assembly and the tangential face of the honing stone in such a position so as to be pivotally balanced and retained in an operating position and in contact with the workpiece surface. It is another object of this invention to have a biasing means such as collapsing springs to retract the honing stones when the unit is de-energized.